Coating composition for mold coat of molded polyurethane resin

ABSTRACT

A coating composition for use in a mold coat coating process wherein the coating composition is previously coated on the molding surface of a mold for polyurethane resin, prior to molding of the polyurethane resin in which the coating composition is transferred onto the surface of the molded polyurethane resin. The coating composition is comprised of a principal component including a resin constituent whose principal ingredient is addition polymer of isophorone diisocyanate and polycarbonate polyol in a content ranging from 8 to 25% by weight of the principal component, and a hardener component including a resin constituent whose principal ingredient is addition polymer of hexamethylene diisocyanate and isophorone diisocyanate in a content ranging from 5 to 100% by weight of the hardener component, thereby improving pot life and weatherability of coating film of the coating composition while contributing shortening of so-called open time in a molding cycle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a coating composition for mold coat of a molded polyurethane resin, and more particularly to such a coating composition which has long pot life and high drying ability while having high weatherability.

2. Description of Prior Art

Hitherto so-called mold coat coating process has been proposed and put into practical use in molding polyurethane resin, in which a coating composition is coated on the inner or molding surface of a mold for polyurethane resin, prior to molding of polyurethane resin; and thereafter the coated coating composition is transferred onto the outer surface of the molded polyurethane resin during molding of the polyurethane resin. There are two types of coating compositions for the mold coat process, i.e., a single liquid type one and a two liquid type one. These types of the mold coat coating compositions will be listed hereinafter.

The single liquid type coating composition (polyurethane lacquer):

a resin constituent: polyurethane compound as addition polymer of glycols (adipate, hexane adipate and the like) and diisocyanates (no yellowing type isophorone diisocyanate, xylene diisocyanate and the like);

a solvent: a mixture of cyclohexanone, methylethyl ketone, xylene, toluene, isopropanol, ethyl acetate, butyl acetate and the like;

a pigment: carbon black (or organic or inorganic colouring pigment to be used for automotive vehicle body in case of other than black):

a dispersant: high molecular weight polycarboxylic acid salt, polyaminoamide phosphate, or alkylamine salt of polycarboxylic acid; and

a light resisting agent: a light stabilizer of benzophenone, benzotriazole or hindered amine.

The two liquid type coating composition:

a principal component:

a resin component (a): polyester polyol (having a molecular weight of 800 to 3,000, hydroxyl value of 12 to 150 and an acid value of not more than 4) which is a polymer of polybasic acid (adipic acid, dicarboxylic acid such as phthalic acid) and polyol of polyhydric alcohol (polyol having OH group at its chain end, such as ethylene glycol, trimethylol propane and the like);

a resin constituent (b): a mixture of polyester polyol (or the resin constituent (a)) and acryl polyol whose principal ingredient is alkyl acylate containing stylene or alkylmethacrylate;

a resin constituent (c): a mixture of the above-mentioned resin component (b) and a copolymer of vinyl chloride and vinyl acetate, or of the above-mentioned resin component (b) and cellulose resin such as cellulose acetate butyrate; and/or

a resin constituent (d): acryl polyol of hydroxyacryl copolymer (having a molecular weight of 3,000 to 10,000, an acid value of 2 to 9 and a hydroxy value of 5 to 30) of acrylate containing hydroxy such as hydroxyalkyl methacrylate and hydroxyalkyl acrylate, and acrylic esters (MMA, butyl methacrylate and the like);

solvent: a mixture of ester solvent such as ethyl acetate, butyl acetate or the like, ketone solvent such as methylisobutyl ketone, methylethyl ketone or the like, and aromatic hydrocarbon such as toluene, xylene or the like, and glycol ether such as cellosolve acetate, butyl cellosolve acetate or the like;

additives: a surface improving agent of polysiloxane copolymer such as silicone oil or the like; a pigment dispersant of alkylamine salt of polycarboxylic acid or polycarboxylic acid salt; and optionally a light stabilizer of benzophenone, benzotriazole or hindered amine;

pigment: inorganic pigment of carbon black, titanium dioxide or the like, organic pigment of Phthalocyanine Blue, quinacridone red or the like, extender pigment of calcium carbonate, barium sulfate or the like, and optionally inorganic substance such as silica or the like and organic substance such as polyethylene wax or the like (these substances are usually used as delustering agent); and

a hardener component:

a resin constituent: aliphatic diisocyanate prepolymer (for example, no yellowing diisocyanate such as hexamethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate or the like), aromatic diisocyanate such as T.D.I, hydrogenenated T.D.I, or so-called soft isocyanate of addition polymer of aliphatic diisocyanate and higher alcohol or polyester to introduce a soft segment into a structure for softening purpose; and

a solvent constituent: ester solvent such as ethyl acetate, butyl acetate or the like, aromatic hydrocarbon such as toluene, xylene or the like, glycol ester such as cellosolve acetate or the like, or a mixture of them.

However, difficulties have been encountered in the above-listed single and two liquid type mold coat coating compositions, as follows: In the above single liquid type mold coat coating composition, the bond of the principal chain of the structure is an ester bond and therefore tends to be broken by hydrolysis. In the above two liquid type mold coat coating composition, the embodiment whose principal component is polyester polyol has ester bonds as the principal chain bonds and has benzene ring in the structure. The embodiment whose principal component is acryl polyol has a rigid molecular chain. Accordingly, both compositions are lower in reaction rate and therefore inferior in drying ability which is required for a coating composition for mold coat. This requires simultaneous use of reaction accelerator in order to improve drying ability, particularly to accelerate initial drying. As a result of use of the reaction accelerator, the single liquid type coating composition is inferior in moisture resistance, hot water resistance and weatherability. Similarly, the above two liquid type coating compositions respectively including, as the principal component, polyester polyol and acryl polyol have defective characteristics as shown in Table 1.

                  TABLE 1                                                          ______________________________________                                                     Conventional coating                                                           composition                                                                      Principal compo-                                                                            Principal                                                         nent:        component:                                          Characteristics                                                                              polyester polyol                                                                            acryl polyol                                        ______________________________________                                         Weatherability                                                                               Bad (chalking                                                                               Good                                                              occurred,                                                                      luster lowered)                                                  Bending ability                                                                              Poor         Poor or bad                                         after weather-             (crack                                              ability test               produced)                                           Pot life      Poor or bad  Bad                                                 Moisture      Poor         Good                                                resistance    (whitened)                                                       Hot water     Poor         Good                                                resistance                                                                     Open time     Shortened    Not                                                                            shortened                                                                      (limited)                                           ______________________________________                                    

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved coating composition for use in a mold coat process, overcoming difficulties encountered in conventional similar coating compositions.

Another object ofthe present invention is to provide animproved coating composition for use in a mold coat process, which is suitable for amolded polyurethane resin, particularly for an automotive vehicle exterior RIM (Reaction Injection Molded) polyurethane resin.

A further object of the present invention is to provide an improved coating composition in use for a mold coat process, which is excellent in physical properties such as weatherability, hot water resistance, moisture resistance and chemicals resistance, and excellent in coating characteristics such as pot life and open time (time between spraying the coating composition and closing a mold in a molding cycle), while providing excellent coated appearance of a resultant polyurethane resin product.

According to the present invention, the coating composition is used in a mold coat process wherein the coating composition is coated initially on the inner or molding surface of a mold prior to molding of polyurethane resin and then during molding the coating composition is transferred onto the surface of the molded polyurethane resin. The coating composition is comprised of a principal component including a resin constituent whose principal ingredient is an addition polymer of at least one compound selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate and hydrogenerated methane diisocyanate, and polycarbonate polyol; and a hardener component including a resin constituent whose principal ingredient is a polymer of diisocyanate.

Hence, by virtue of the principal component of the present invention, (a) Ester or ester bond is removed or reduced, and therefore the coating composition is excellent in resistance to hydrolysis decomposition; (b) Bonding energy in the principal bond is higher; (c) Molecular weight is higher (more than 10,000), and (d) Coating film is higher in strength or excellent in balance between extension (not less than 100%) and tensile strength (200 kg/cm²), thereby providing a high weatherability coating film.

By virtue of the hardener component of the present invention, a reaction system in which reaction occurs under the action of cross linking agent becomes possible after formation of the coating film upon evaporation of the solvent. This enhances two contradictary functions of prolongation of pot life and quick drying, thereby making it possible to shorten the open time. Accordingly, operational efficiency of coating or painting is improved. Additionally, by using the thinner having a good diluting ability for the principal and hardener components and having a high evaporation rate, the operational efficiency of coating or painting is further improved.

Furthermore, the coating composition according to the present invention solidifies within a short period of time and offers a predetermined strength, and therefore it does not flow under the pressure of polyurethane resin or molding material when the polyurethane resin is poured to the cavity of the mold. Besides, by suitably increasing molecular weight of the principal composition, the solvent is easily separable from the resin constituent while concordance of the coating film with the mold releasing agent is good, thus providing good appearance of the coating film.

Consequently, the coating film of the coating composition of the present invention has a high weatherability which is required for the mold coat or coating film of a molded RIM-polyurethane resin product. Therefore, the coating composition of the present invention is suitable for automotive exterior plastic parts and for a variety of paints.

Moreover, since the coating composition of the present invention has a quick drying ability though having a long pot life, the open time can be shortened. As a result, the time of a molding cycle is greatly shortened. In addition, coloring of the coating composition of the present invention can be facilitated thereby making it possible to exhibit the feeling of an integrated or one-piece member even with other parts, thereby offering a good design effect while providing lustrous molded plastic products.

DETAILED DESCRIPTION OF THE INVENTION

A coating composition according to the present invention is used in a mold coat coating process wherein the coating composition is coated initially on the inner or molding surface of a mold for polyurethane resin, prior to molding of the polyurethane resin, in which the coating composition is transferred onto the surface of the molded polyurethane resin. The coating composition is comprised of a principal component including a resin constituent whose principal ingredient is an addition polymer (referred to as "urethane polyol" hereinafter) of at least one selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate and hydrogenated methane diisocyanate, and polycarbonate polyol; and a hardener component including a resin constituent whose principal ingredient contains polymer of aliphatic diisocyanate.

The coating composition is preferably further comprised of a thinner component for diluting the coating composition, including as a principal ingredient a mixture of ketone, aromatic hyrocarbon, ester and glycol.

It is more preferable that the composition or blending ratio of the principal component is defined as shown in Table 2, and that of the hardener component is defined as shown in Table 3.

                  TABLE 2                                                          ______________________________________                                         Constituent      Content                                                       ______________________________________                                         "Urethane polyol"                                                                               8 to 25 wt %                                                  Methylethyl ketone                                                                              30 to 45.5 wt %                                               Cyclohexane      30 to 45.5 wt %                                               Pigment such as carbon                                                                          1 to 4 wt %                                                   Pigment dispersant                                                                              0.2 to 1.5 wt %                                               ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                         Constituent     Content                                                        ______________________________________                                         Aliphatic diisocyanate                                                                         5 to 100 wt %                                                  Ethyl acetate   0 to 47.5 wt %                                                 Toluene         0 to 47.5 wt %                                                 Reaction accelerator                                                                           0.005 to 1.0 wt %                                              ______________________________________                                    

EXAMPLE

To evaluate the coating composition of the present invention, Examples of the present invention will be discussed hereinafter in comparison with Comparative Examples which are not within the scope of the present invention, with reference to Tables 4 and 5 in which content is indicated in "part by weight".

EXAMPLE 1

First the principal component and the hardener component (as indicated in Table 4) were mixed and stirred in a container to be sufficiently blended. The thinner (as indicate in Table 4) for dilution purpose was added into the container and stirred to prepare the coating composition having a viscosity of 12 to 15 seconds and a non-volatile content of 9.5 to 11%. Subsequently, the prepared coating composition was sprayed onto the inner or molding surface (whose temperature was adjusted at 65° to 72° C.) of a mold by using an air spray gun having a nozzle opening diameter of 0.8 to 1.3 mm under a condition of air pressure of 2.5 to 3 kg/cm² and a discharge amount of 60 to 100 cc/min, to obtain a coating composition film having a predetermined thickness. The molding surface of the mold had been already coated with mold releasing agent before spraying the coating composition. After spraying the coating composition, the mold was immediately closed to confine therein a cavity for molding, and then polyurethane resin as the molding material was poured into the molding cavity.

Upon lapse of 30 seconds (or after completion of reaction and hardening of the molding material) after pouring of the molding material, the mold was opened to take out a molded product whose surface was coated with a mold coat (or the hardened coating composition). The mold coat was formed by being transferred from the molding surface of the mold onto the surface of the molded product.

It is to be noted that the above experiment was conducted under conditions of Examples 1 and 1' shown in Table 6.

The principal component and the hardener component used in Example 1 are shown in Table 4 and described in detail below.

The principal component

Ingredient: Addition polymer of isophorone diisocyanate and polycarbonate polyol;

Characteristics:

Molecular weight: 15,000 to 20,000

OH content: Not more than 4%

Acid value: Not less than 1

General formula: Basic frame ##STR1## Extension/tensile strength: 450-500%/350-400 kg/cm²

Feature: Higher in resistance against hydrolysis decomposition and in bonding energy; and highly balanced in extendability and strength of coating film.

It has been confirmed that similar characteristics and feature was obtained also in case of using addition polymer of polycarbonate polyol and a mixture of at least two of isophorone diisocyanate, hexamethylene diisocyanate and hydrogenated methane diisocyanate, or in case of using addition polymer of polycarbonate polyol and one of hexamethylene diisocyanate and hydrogenated methane diisocyanate. In the characteristics and feature, the prepared principal component was higher in molecular weight and in resistance to hydrolysis decomposition depending on the fact that ester bond was removed, and higher in bond energy.

The hardener component

Ingredient: Addition polymer of hexamethylene diisocyanate and isophorone diisocyanate;

Characteristics: NCO content: 15 to 16%

Feature: No yellowing and higher drying ability

It will be appreciated that addition polymer of other aliphatic diisocyanate (for example, no yellowing diisocyanate such as xylene diisocyanate) will be used as the hardener component.

EXAMPLES 2 TO 4 AND COMPARATIVE EXAMPLES 1 TO 5

Experiments of Examples 2 to 4 were conducted similarly to that of Example 1, using the principal and hardener components and the dilution thinner as shown in Tables 4 and 5 and under conditions of Examples 2 to 4 in Table 6 thereby to obtain resultant molded products with the coating films of the coating compositions. Additionally, experiments of Comparative Examples 1 to 5 were conducted similarly to that of Example 1, using the principal and hardener components and dilusion thinner as shown in Table 5 and under conditions of Comparative Examples 1 to 5 in Table 7 thereby to obtain resultant molded products with the coating films of the coating compositions.

Evaluation Test

The thus obtained coating films of the resultant molded products of Examples 1 to 4 and Comparative Examples 1 to 5 were subjected to evaluation tests as shown in Tables 6 and 7 in order to evaluate the coating compositions according to present invention.

As appreciated from the evaluation test results of Tables 6 and 7, it has been confirmed that the coating films of the coating compositions of Examples 1, 1', 2, 3 and 4 (according to the present invention) are excellent in weatherability, long in pot life and short in open time in molding cycle, as compared with those of Comparative Examples 1, 2, 3, 4 and 5 (not within the scope of the present invention).

                                      TABLE 4                                      __________________________________________________________________________     Principal component (part by weight)                                                Resin     Solvent             Reaction         Light resist-              Sample                                                                              constituent                                                                              constituent                                                                              Pigment   accelerator                                                                          Dispersant ing                        __________________________________________________________________________                                                         agent                      Example                                                                             Addition                                                                              20.0                                                                              Methylethyl-                                                                          39.0                                                                              Channel-type                                                                          2.0                                                                               Nil   Salt of long                                                                           0.5                                                                               Nil                        1    polymer of                                                                               kethone   carbon black    chain poly-                                isophorone                                                                               Cyclohexane                                                                           39.0               aminoamide and                             diisocyanate                        salt of polar                              and poly-                           acid ester                                 carbonate                                                                      polyol                                                                    Example                                                                             Addition                                                                              20.0                                                                              Methylethyl-                                                                          30.0                                                                              Furnace-type                                                                          2.5                                                                               Nil   Polyamide                                                                              0.5                                                                               Nil                        2    polymer of                                                                               kethone   carbon black                                               isophorone                                                                               Cylcohexane                                                                           25.0                                                          diisocyanate                                                                             Butyl acetate                                                                         20.0                                                          and poly- Toluene                                                                               25.0                                                          carbonate                                                                      polyol                                                                    Example                                                                             Addition                                                                              20.0                                                                              Methylethyl-                                                                          39.0                                                                              Channel-type                                                                          2.0                                                                               Nil   Salt of long                                                                           0.5                                                                               Benzotriazol                                                                           1.0                3    polymer of                                                                               kethone   carbon black    chain poly-                                                                               (hydroxy-t-                     isophorone                                                                               Cyclohexane                                                                           39.0         aminoamide    octylphenyl)                       diisocyanate                        and salt of                                and poly-                           polar acid                                 carbonate                           ester                                 Example                                                                             Addition                                                                              20.0                                                                              Methylethyl-                                                                          32.0                                                                              Channel-type                                                                          2.5                                                                               Nil   Salt of poly-                                                                          1.0                                                                               Hydroxy-t-                                                                             1.0                4    polymer of                                                                               kethone   carbon black    carboxylic octylphenyl                     isophorone                                                                               Cyclohexane                                                                           46.0               acid       benzotri-                       diisocyanate                                                                             Butyl acetate             (Trade name:                                                                              azole                           and poly-                           AT203      Tris-butyl-                                                                            0.5                     carbonate                                      hydroxy-                        polyol                                         dimethyl-                                                                      isocyanuric                                                                    acid                       __________________________________________________________________________                          Hardener component (part by weight)                                            Resin      Solvent   Reaction Dillution thinner                           Sample                                                                              constituent                                                                               constituent                                                                              accelerator                                                                             (part by                    __________________________________________________________________________                                                        weight)                                     Example                                                                             Addition                                                                               18.0                                                                              Ethyl acetate                                                                         38.0                                                                              Dibutyltine                                                                          0.05                                                                              Methylethyl-                                                                            24.5                               1    polymer of Toluene                                                                               44.0                                                                              dilaurate                                                                               kethone  24.5                                    hexamethylene                 Cyclohexane                                                                              7.0                                    diisocyanate                  Toluene  28.0                                    and iso-                      Xylene   18.0                                    phorone                       Butyl    14.0                                    diisocyanate                  acetate                                     Example                                                                             Addition                                                                               18.0                                                                              Ethyl acetate                                                                         38.0                                                                              Dibutyltine                                                                          0.05                                                                              Ethyl     2.0                               2    polymer of Toluene                                                                               44.0                                                                              dilaurate                                                                               acetate                                          hexamethylene                 Cellosolve                                                                               6.0                                    diisocyanate                  acetate                                          and iso-                      <or>                                             phorone                       Methylethyl                                                                             35.0                                    diisocyanate                  kethone                                     Example                                                                             Addition                                                                               18.0                                                                              Ethyl acetate                                                                         38.0                                                                              Dibutyltine                                                                          0.05                                                                              Cyclohexane                                                                             10.0                               3    polymer of Toluene                                                                               44.0                                                                              dilaurate                                                                               Toluene  35.0                                    hexamethylene                 Butyl    20.0                                    and iso-                      acetate                                          phorone                                                                        diisocyanate                                                              Example                                                                             Isocyanurate                                                                           15.0                                                                              Ethyl acetate                                                                         85.0                                                                              Nil                                                  4    type of                                                                        hexamethylene                                                                  diisocyanate                                                                   (Trade name:                                                                   Cholonate EH)                                             __________________________________________________________________________

    TABLE 5       Hardener component  Principal component (part by weight)  Solvent      Dillution thinner  Resin Solvent  Reaction  Light resist- Resin Consti-      Dillution thinner Sample constituent constituent Pigment accelerator      Dispersant ing agent constituent tuent (part by weight)        Compar- Acryl polyol 24.0 Toluene 23.0 Silica 8.0 Dibutyltin 0.03 Salt      of long 0.5 Benzotriazole 0.5 Prepolymer of 81.0 Toluene  9.0 Ethyl      acetate 14.0 ative as copolymer  Xylene 20.0 powder  octate  chain poly-       1,3,5-tris-  0.15 hexamethylene  Ethyl 10.0 Cellosolve 10.0 example of      hydroxy-  Butyl acetate 14.0 Carbon black 1.7   aminoamide and  isocyanur      ic  diisocyanate  acetate  acetate 1 ethylmetha-  Cellosolve  9.3      (channel    polar acid  acid  and polyester    Toluene 42.0  crylate,      acetate  type)    ester    polyol    Xylene 24.0  methylmetha-           Methylisobutyl- 10.0  crylate and                kethone  butylacryl      ate Compar- Mixture of 22.0 Toluene 20.0 Silica 4.0 Dibutyltin 0.02 Salt      of poly- 0.5 Benzotriazole 1.0 Xylene 25.0 Ethyl 75.0 Ethyl acetate 25.0      ative polyester  Xylene 21.0 powder  octate  carboxylic acid    diisocyan      ate  acetate  Toluene 30.0 example polyol and  Ethyl acetate 15.0      Polyethylene 2.5           Methylisobutyl- 25.0 2 copolymer of  Methyl-      6.0 wax            kethone  vinyl chloride  isobutylketon  Carbon black      2.0           Butyl acetate 20.0  and vinyl  Cellosolve  8.5 (channel      acetate  acetate  type) Compar- Mixture of 23.0 Toluene 20.0 Silica 5.0      Dibutyltin 0.02 Salt of poly- 0.5 Benzotriazole 0.5 Xylene 25.0 Ethyl      75.0 ative polyester  Xylene 21.0 powder  octate  carboxylic acid      diisocyanate  acetate example polyol and  Ethyl acetate 15.0 Polyethylene       3.0 3 hydroxy-  Methyl-   6.0 wax  acrylate  isobutylketon  Carbon      black 2.5  containing  Cellosolve  4.5 (channel  stylen  acetate  type)      Compar- Mixture of 23.0 Toluene 20.0 Silica 5.0 Dibutyltin 0.02 Salt of      poly- 0.5 Benzotriazole 0.5 Toluene 25.0 Ethyl 75.0 ative polyester      Xylene 21.0 powder  octate  carboxylic acid    diisocyanate  acetate      example polyol and  Ethyl acetate 15.0 Polyethylene 3.0 4 hydroxy-      Methyl-  6.0 wax  acrylate  isobutylketon  Carbon black 2.5  containing      Cellosolve  4.5 (channel  stylen  acetate  type) Compar- Polyurethane      20.0 Methylethyl- 25.0 Silica 2.5 Nil  Salt of long 0.5 Benzotriazole      0.5 Addition polymer 20.0 Toluene 25.0 Toluene 25.0 ative compound as      kethone  powder    chain poly-    of hexamethylene  Ethyl 45.0 Methylethy      l- 35.0 example addition  Cyclohexane 20.0 Polyethylene 2.0   aminoamide      and    diisocyanate and  acetate  kethone 5 polymer of  Isopropyl  8.0      wax    polar acid    isophorone    Diacetone alcohol 10.0  glycols and      alcohol  Carbon black 2.0   ester    diisocyanate    Cyclohexanone 10.0      diisocyanate  Diacetone  5.5 (channel            Methylisobutyl 20.0      (no yellowing  alcohol  type)            ketone  type)  Methyl- 15.0      iso-    butylketone

                                      TABLE 6                                      __________________________________________________________________________                     1                                                              Item         Example 1                                                                             Example 2                                                                             Example 3                                                                             Example 4                                                                             Example 5                             __________________________________________________________________________     Blending                                                                            Principal                                                                              100    100    100    100    100                                   ratio                                                                               component                                                                 (part by                                                                            Hardener                                                                                10     10     10     10     10                                   weight)                                                                             component                                                                      Thinner 130    130    130    130    130                                   NV during coating                                                                               9.7%                                                                                  9.7%                                                                                  9.7%                                                                                 10.7%                                                                                  9.7%                              Thickness of dried                                                                          10 to 20μ                                                                          10 to 20μ                                                                          10 to 20μ                                                                          10 to 20μ                                                                          20 to 30μ                          coating film                                                                   Molding                                                                             Metal mold                                                                             70 to 72° C.                                                                   70 to 72° C.                                                                   70 to 72° C.                                                                   70 to 72° C.                                                                   70 to 72° C.                   condition                                                                           temperature                                                               of poly-                                                                            Curing time                                                                            30 to 40 sec.                                                                         30 to 40 sec.                                                                         30 to 40 sec.                                                                         30 to 40 sec.                                                                         30 to 40 sec.                         urethane                                                                            Mold releasing                                                                         Silicone wax                                                                          Silicone wax                                                                          Silicone wax                                                                          Silicone wax                                                                          Silicone wax                          resin                                                                               agent                                                                     product                                                                             Open time                                                                               5 to 30 sec.                                                                          5 to 30 sec.                                                                          5 to 30 sec.                                                                          5 to 30 sec.                                                                         10 to 30 sec.                         to be                                                                          coated                                                                         with                                                                           coating                                                                        composi-                                                                       tion                                                                           Evalua-                                                                             Appearance                                                                             Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                             tion test                                                                           Adherence to                                                                           Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                             result of                                                                           molded poly-                                                              coating                                                                             ethylene resin                                                            film of                                                                             Moisture                                                                               Good to                                                                               Good to                                                                               Good to                                                                               Good to                                                                               Good to                               coating                                                                             resistance                                                                             excellent                                                                             excellent                                                                             excellent                                                                             excellent                                                                             excellent                             composi-                                                                            Hot water                                                                              Good to                                                                               Good to                                                                               Good to                                                                               Good to                                                                               Good to                               tion resistance                                                                             excellent                                                                             excellent                                                                             excellent                                                                             excellent                                                                             excellent                                  Chemicals                                                                              Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                  resistance                                                                     Heat resistance                                                                        Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                  Weatherability                                                                         Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                                                             Excellent                                  S-W · O-M                                                                     ΔE 1.6                                                                          ΔE 1.5                                                                          ΔE 1.45                                                                         ΔE 1.56                                                                         ΔE 1.5                               2000 hrs.                                                                              GR 19.8%                                                                              GR 18.5%                                                                              GR 20.0%                                                                              GR 19.5%                                                                              GR 19.0%                                           (No chalking)                                                                         (No chalking)                                                                         (No chalking)                                                                         (No chalking)                                                                         (No chalking)                                      Bendability:                                                                          Bendability:                                                                          Bendability:                                                                          Bendability:                                                                          Bendability:                                       Good   Good   Good   Good   Good                                       QUV     ΔE 9.5                                                                          ΔE 5.1                                                                          ΔE 6.4                                                                          ΔE 8.3                                                                          ΔE 7.6                               2000 hrs.                                                                              GR 50.5%                                                                              GR 51.0%                                                                              GR 52.5%                                                                              GR 49.5%                                                                              GR 51.0%                                           (No chalking)                                                                         (No chalking)                                                                         (No chalking)                                                                         (No chalking)                                                                         (No chalking)                                      Bendability:                                                                          Bendability:                                                                          Bendability:                                                                          Bendability:                                                                          Bendability:                                       Good   Good   Good   Good   Good                                       Pot life                                                                                8 to 10 hrs.                                                                          8 to 10 hrs.                                                                          8 to 10 hrs.                                                                          8 to 10 hrs.                                                                          8 to 10 hrs.                         __________________________________________________________________________

                                      TABLE 7                                      __________________________________________________________________________                  Comparative                                                                            Comparative                                                                            Comparative                                                                            Comparative                                                                            Comparative                       Item         example 1                                                                              example 2                                                                              example 3                                                                              example 4                                                                              example 5                         __________________________________________________________________________     Blending                                                                            Principal                                                                              100     100     100     100     100                               ratio                                                                               component                                                                 (part by                                                                            Hardener                                                                               15      16      16      15       10                               weight)                                                                             component                                                                      Thinner 70      30      40      30      100                               NV during coating                                                                             24.0%   23.0%   24.0%   24.0%    13.5%                          Thickness of dried                                                                          15 to 20μ                                                                           15 to 20μ                                                                           15 to 20μ                                                                           15 to 20μ                                                                           10 to 20μ                      coating film                                                                   Molding                                                                             Metal mold                                                                             70 to 72° C.                                                                    70 to 72° C.                                                                    70 to 72° C.                                                                    70 to 72° C.                                                                    70 to 72° C.               condition                                                                           temperature                                                               of poly-                                                                            Curing time                                                                            30 to 40 sec.                                                                          30 to 40 sec.                                                                          30 to 40 sec.                                                                          30 to 40 sec.                                                                          30 to 40 sec.                     urethane                                                                            Mold releasing                                                                         Silicone wax                                                                           Silicone wax                                                                           Silicone wax                                                                           Silicone wax                                                                           Silicone wax                      resin                                                                               agent                                                                     product                                                                             Open time                                                                              30 sec. to                                                                             30 sec. to                                                                             30 sec. to                                                                             30 sec. to                                                                             30 sec. to                        to be        2 min.  2 min.  2 min.  2 min.  2 min.                            coated                                                                         with                                                                           coating                                                                        composi-                                                                       tion                                                                           Evalua-                                                                             Appearance                                                                             Permissible                                                                            Good    Good    Good    Good                              tion test    to good                                                           result of                                                                           Adherence to                                                                           Excellent                                                                              Excellent                                                                              Excellent                                                                              Excellent                                                                              Excellent                         coating                                                                             molded poly-                                                              composi-                                                                            ethylene resin                                                            tion Moisture                                                                               Excellent                                                                              Permissible                                                                            Good to Permissible                                                                            Bad to                                 resistance      to good excellent                                                                              to good Permissible                            Hot water                                                                              Excellent                                                                              Permissible                                                                            Good to Permissible                                                                            Bad to                                 resistance      to good excelelnt                                                                              to good Permissible                            Chemicals                                                                              Excellent                                                                              Permissible                                                                            Excellent                                                                              Permissible                                                                            Good                                   resistance      to good         to good                                        Heat resistance                                                                        Excellent                                                                              Good    Good    Permissible                                                                            Good                                   Weatherability                                                                         Bad     Bad     Bad     Bad     Bad                                    S-W · O-M                                                                     E 4.5   E 6.5   E 6.0   E 12.5  E 8.6                                  2000 hrs.                                                                              GR 15.5%                                                                               GR 5.0% GR 10.5%                                                                               GR 3.0% GR 5.4%                                        Crack occurred                                                                         (Chalking                                                                              (Chalking                                                                              (Chalking                                                                              (Chalking                                      upon bending                                                                           occurred)                                                                              occurred)                                                                              occurred)                                                                              occurred)                                              Crack occurred                                                                         Crack occurred                                                                         Crack occurred                                                                         Crack occurred                                         upon bending                                                                           upon bending                                                                           upon bending                                                                           upon bending                           QUV     ΔE 4.8                                                                           ΔE 7.2                                                                           ΔE 8.5                                                                           ΔE 11.6                                                                          ΔE 9.4                           2000 hrs.                                                                              GR 16.5%                                                                               GR 4.5% GR 8.0% GR 2.0% GR 3.0%                                        Crack occured                                                                          Crack occurred                                                                         Crack occurred                                                                         (Chalking                                                                              (Chalking                                      upon bending                                                                           upon bending                                                                           upon bending                                                                           occurred)                                                                              occurred)                                                              Crack occurred                                                                         Crack occurred                                                         upon bending                                                                           upon bending                           Pot life                                                                               3 to 4 hrs.                                                                            5 to 6 hrs.                                                                            5 to 6 hrs.                                                                            4 to 5 hrs.                                                                            2 to 9 hrs.                       __________________________________________________________________________ 

What is claimed is:
 1. A coating composition for use in a mold coat coating process, wherein said coating process includes the steps of initially coating said coating composition the inner surface of a mold prior to molding of a polyurethane resin and subsequently transferring during molding said coating composition onto the surface of the molded polyurethane resin, said coating composition comprising:(a) a principal component comprising a resin constituent that comprises units of (i) at least one selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate and hydrogenated methane diisocyanate, and (ii) a polycarbonate polyol; and (b) a hardener component comprising an addition polymer including an aliphatic diisocyanate.
 2. A coating composition as claimed in claim 1, further comprising a thinner composition for diluting said coating composition, said thinner composition comprising a mixture of at least one ketone, at least one aromatic hydrocarbon and at least one ester.
 3. A coating composition as claimed in claim 1, wherein said resin constituent is present in said principal component in an amount ranging from 8 to 25% by weight of said principal component.
 4. A coating composition as claimed in claim 1, wherein said principal component further comprises a solvent constituent comprising at least one of methyl ethyl ketone and cyclohexanone.
 5. A coating composition as claimed in claim 4, wherein each of methyl ethyl ketone and cyclohexanone is present in an amount ranging from 30 to 45.5% by weight of said principal component.
 6. A coating composition as claimed in claim 1, wherein said principal component further comprises a pigment in an amount ranging from 1 to 4% by weight of said principal component.
 7. A coating composition as claimed in claim 6, wherein said pigment is carbon black.
 8. A coating composition as claimed in claim 6, wherein said principal component further comprises a dispersant for said pigment, in an amount ranging from 0.2 to 1.5% by weight of said principal component.
 9. A coating composition as claimed in claim 1, wherein said aliphatic diisocyanate is present in an amount ranging from 5 to 100% by weight of said hardener component.
 10. A coating composition as claimed in claim 1, wherein said hardener component further comprises a solvent constituent comprising at least one of ethyl acetate and toluene.
 11. A coating composition as claimed in claim 10, wherein each of said ethyl acetate and toluene is present in an amount not exceeding 47.5% by weight of said hardener component.
 12. A coating composition as claimed in claim 1, wherein said hardener component further comprises a reaction accelerator in an amount ranging from 0.005 to 1.0% by weight of said hardener component.
 13. A coating composition as claimed in claim 12, wherein asid reaction accelerator is dibutyltin dilaurate.
 14. A coating composition as claimed in claim 2, wherein said thinner composition comprises a mixture of methyl ethyl, cyclohexanone, toluene and butyl acetate.
 15. A coating composition as claimed in claim 1, wherein said hardener component comprises an addition polymer of hexamethylene diisocyanate and isophorone diisocyanate. 